1. Field of the Invention
The present invention relates to a downhole tool. More particularly, the invention relates to a bridge plug for sealing the interior of a wellbore at a predetermined location.
2. Background of the Related Art
An oil or gas well includes a wellbore extending from the surface of the well to some depth therebelow. Typically, the wellbore is lined with tubular or casing to strengthen the sides of the borehole and isolate the interior of the casing from the earthen walls therearound. In order to access production fluid in a formation adjacent the wellbore, the casing is perforated, allowing the production fluid to enter the wellbore and be retrieved at the surface of the well. A single well may have multiple levels of production zones. In order to isolate oil from a specific zone, a tool, known as a bridge plug is placed within the wellbore to isolate the upper and lower portions of the zones. Bridge plugs also create a pressure seal in the wellbore allowing fluid pressure to be applied to the wellbore to treat the isolated formation with pressurized fluids or solids.
FIG. 1 is a section view of a well 10 with a wellbore 12 having a bridge plug 15 disposed within the wellbore casing 20. The bridge plug 15 is typically attached to a setting tool and run into the hole on wire line or tubing (not shown), and then actuated with some type of pyrotechnic or hydraulic system. As illustrated in FIG. 1, the wellbore is sealed above and below the bridge plug so that oil migrating into the wellbore through perforations 23 will be directed to the surface of the well.
FIG. 2 is a cross sectional view of a prior art bridge plug 50. The bridge plug 50 generally includes a body portion 80, a sealing member 52 to seal an annular area between the bridge plug 50 and the inside wall of casing (not shown) therearound and slips 56,61. The sealing member 52 is disposed between an upper retaining portion 55 and a lower retaining portion 60. In operation, axial forces are applied to slip 56 while the body and slip 61 are held in a fixed position. As the slip 56 moves down in relation to the body 80 and slip 61, the sealing member is actuated and the slips 56,61 are driven up cones 55,60. In the prior art bridge plug of FIG. 2, the slips are xe2x80x9cuni-directionalxe2x80x9d and are most effective against axial forces applied to the bridge plug in a single direction. The movement of the cones and slips also axially compress and radially expand the sealing member 52 thereby forcing the sealing portion radially outwardly from the plug to contact the inner surface of the well bore casing. The compressed sealing member 52 provides a fluid seal to prevent the movement of fluids across the bridge plug.
There are problems associated with prior art bridge plugs like the one shown in FIG. 2. Bridge plugs are intended to be temporary and must be removed in order to access the wellbore therebelow. Rather than de-actuate the bridge plugs and bring them to the surface of the well, they are more typically destroyed with a rotating milling or drilling device run into the well at the end of a tubular string. As the mill contacts the bridge plug, the plug, usually constructed of cast iron, aluminum or composite material, is xe2x80x9cdrilled upxe2x80x9d or reduced to small pieces which are easily washed out of the wellbore or simply left at the bottom of the wellbore. The more parts making up a bridge plug, the longer the milling operation takes. Likewise, the longer the bridge plug, the longer the drilling operation will take.
Another problem of prior art bridge plugs is related to the location of the slips in the body of the plug. Since the bridge plug is held into place by the slips, the bridge plug breaks free of the wellbore and falls when the milling device reaches and loosens the slips. Depending upon where the slips are located in relation to the top of the bridge plug, a large portion of the plug can remain in one piece when the plug falls. Large pieces of bridge plug in a wellbore can cause delays if other plugs or tools are installed in the wellbore therebelow.
There is a need therefore, for a bridge plug which can effectively seal a wellbore and remain effective when subjected to pressures from above or below when in use. There is a further need for a bridge plug which can be more completely drilled up, resulting in a smaller portion of the plug falling down the wellbore. There is yet a further need for a bridge plug having fewer parts and a reduced length which allows faster dill up times to remove the set plug from the wellbore.
The present invention relates to a bridge plug for use in a wellbore to isolate an upper portion of the wellbore from a lower portion. The bridge plug is run into the wellbore on wireline or run-in tubular and then set in the wellbore at a predetermined depth. In one aspect of the invention, the bridge plug includes a cylindrical body having a longitudinal bore therethrough which is sealed in at least one direction to the passage of fluid. A first and second lock ring assemblies are installed on the outer surface of the body and are designed to move in a single direction with respect to the body. A bidirectional slip member which provides resistance to axial forces in two directions and a sealing member are also located on the exterior of the body.
The sealing member is disposed between the first and second lock ring assemblies and is actuated by movement of the first lock ring towards the second lock ring. The slip is a circular member with teeth on the outer surface thereof and is arranged to break into segments when radial pressure is applied thereto. The slip is actuated by force applied thereto from a sloped shoulder formed on the body and a sloped surface formed on the second lock ring assembly. In operation, both lock ring assemblies move toward the shoulder as the plug is set in the wellbore, thereby setting the sealing member therebetween and setting the slip between the second lock ring assembly and the shoulder.
In another aspect of the invention, a bridge plug includes a first and second lock ring assemblies movable in opposing directions along the surface of the body. A first lock ring assembly provides force to actuate a sealing member and a bidirectional slip member. The second lock ring assembly provides a means to further actuate the slip and sealing member in the event pressure is applied to the bridge plug from above while it is installed in a wellbore. The bridge plug can be removed from the wellbore by milling without a substantial portion of the unmilled bridge plug falling to the bottom of the wellbore.